Composition for cleaning metal such as aluminum and magnesium



Patented Aug. 7, 1945 UNITED; STATES PATENT comrggrrron mu. soon- OFFICE Jamar. Hart, to. Angelou, ouu 'munor to Kellie Products, Inc., LosAngeics, Call! a cocporation of California No Drawing. Application October 23, 1940,

' 8I|8IHO.382,410

comma. (erase-13s) 1 This invention relates to a'composition for cleaning metals, such as aluminum and magf nesium, and refers particularly to a composition suitable for preparing aluminum for an anodizing treatmen't, or for preparing magnesium preliminary to a chromidizlng treatment, or for re-' moving coatings from such materials.

In order to protect aluminum from the outside elements, it is commonly subjected to an anodizing treatment for the purpose of building up the coating of aluminum oxide. Preliminary to such an anodizing treatment. the aluminumshould be thoroughly cleaned. Previous to the present invention, difliculty was experienced in rapidly cleaning aluminum. Most cleansing agentsdepend upon the action of an alkali, and

aluminum may be attacked rapidly by an alkali,

resulting in etching. a

Similar diiflculties are experienced in preparing magnesium for a chromidizing operation.

It is also a practice to coat aluminum with different coating materials for the purpose of preserving the aluminum. For example, primer coating may be applied, such as a zinc-chromate primer. Where it has been found desirable to V remove such primer coating, the art. previous to the present invention experienced great diiliculties.

It is. a general object of the present inventionsilicates have beenpreviously employed in cleans capable of converting all of the alkali silicates present and all of the acid phosphates present into the trl-phosphat'e and into the acid meta silicate salt. For example, sodium metasilicate. NazO.SiO-.-.5H:O, may be combined with disodium phosphate in the stoichiometric proportions of and when so combined the following reaction may theoretically take place:' L

A substantially equivalent composition for the purposes of the present invention may be produced from combining monosodium phosphate,

NaH2PO4, with sodium orthosilicate, Naisioi, in which case the stoichiometric proportions re-.

quired are three mols of N8-H3P04 with two mols of NaHSiOr, and the following reaction is theoretically possible:

' Similarly, a' substantially equivalent composi-- tion for the purposes of the present invention may be made by combining disodium phosphate,

NazHPm, with'sodium orthosilicate, NarSiOa, in which case the correct stoichiometrlc proportion to be employed is 3 mols of N4 for each moi of NEASiQ-i, and the following reaction may theoretically take place:

The proportions of ingredients are critical to the production of a. composition which will not etch aluminum. The critical proportions are that the alkali silicates and the acid phosphams present must be such as to correspond to the compounds NaHSiO: and NasPOi; or, stating the relationship on the basis of the anhydrides, for each moi foi P205 there must be 3 mole of New, and for log compounds but as previously employed have v always possessed a pronounced tendency to attack or etch metals such as aluminum or magnesium. Likewise, acid phosphates exhibita tendency to attack or etch aluminum. It has been discovered, however, that by properly combining such 'substances the tendency of the materials for attacking the metals'is eliminated without interiering with their cleansing properties.

The proper proportions for combining the alkali silicates with the acid phosphates is in such stoichiometric proportions as to theoretically be so each -2 mols of 8102 present there must be i moi of NaaO present. It the ingredients are not present in substantially these critical relationships, the solution will in effect etch-aluminum.

From the foregoing equations, it will be seen that various alkali silicates may be combined with various acid phosphates, each to produce solutions the composition of which can be representedi as composed exclusively of trisodium Phosphate and acid sodium metasilicate. Salts of other alkalis than sodium may be substituted, such as potassium salts ii desired, although such salts are not believed to have any advantage over the employment of sodium salts and are merely.

.of the composition per more expensive.

In order that the composition should the cleansing properties desired while having substantially no etching effect on aluminum and magnesium, the stoichiometric proportions above indicated should be fairly closely followed, although some variation therefrom may be tolerated in practice. As an example of the permissible variation, the stoichiometrlc proportions when employing sodium metasilicate,

suillcient to employ merely an aqueous solution.

of the composition. For example, 2 to 8 ounces gallon of water may be employed. The cleanin operation is preferably eil'ected by dipping the aluminum to be cleaned into the aqueous solution of the composition, which is preferably maintained at a temperature of, for example, 180 to 212 F., a suitable clean- 7 ing may be effected in from 30 seconds to minutes. In certain cases, it may be desirable to add to the solution or cleansing composition a surface active agent or a surface tension reducing material for the purpose of facilitating a wetting of the aluminum by the cleansing solution. Various surface active agents may be employed, such for example as surface active agent of the alkyl aryl sulphonate type. 1

Where the composition is to be employed for removing coating materials, such as the zinc chromate primer from aluminum, it should contain additional ingredients. In such a case. I add to the aqueous solution a material, such for example as starch, for the purpose of making the cleaning commition into a thin paste. In such case, also, it may be desirable to add a solvent for any gums, etc., which may be on the metals to be treated. and I find solvents of the butyl Cellosoive" (ethylene glycol monobutyl ether) type to be a suitable solvent for such purpose. It

is also desirable in such cases to employ in the composition a pigment in orderthat the presence of'the composition on the metal to be cleaned may be more readily detected. For example, for the purpose of removing coatings from aluminum, I have found the following particular compositions to be highly effective:

Percent Sodium metasilicate (N820.S102.5H20) 9 Anhydrous disodium phosphate (Nari-IP04) 6 Starch 3 Surface active agent l Pigment (Turkey red umber) 5 Solvent 6 and the balance of 70% B20.

The above-indicated composition may be applied for removing coatings simply by sp ay n the composition on the aluminum from which the coating is tobe removed. In contrast to the use of ordinary paint removers, which in order to et- ,mate primer is to be removed salts of orthophosphoric fectively clean the metal must be wiped 01! am removed with rags. the coating composition 0) the present invention after being sprayed upor themetaltobecleanedmaywithinashortpcriod of time thereafter be removed merely by washing the same of! with water. Where zinc chrofrom aluminum, it will be found that the primer coat will be peeled cleanly from the aluminum when the coating composition of the present invention is removed from themetal by washing the same oi! with water. The composition of the present invention has the unusual property of affording an alkali cleaning agent for aluminum or maggesium which may he brought into prolonged ntact therewith, even at elevated temperature if desired, without danger of the composition attacking or etching the metal.

I claim:

1. A composition for cleaning such metals as aluminum or magnesium. which composition comprises an aqueous solution containing sodium acid and silicic acid in substantially the stoichiomctric proportions of three mols of NazO per mol of Pros and one moi of NazO per two mols of 810:.

2. A composition for cleaning such metals is aluminum or magnesium, which composition 'aluminum or magnesium, which composition comprises an aqueous solution containing sodium salts of orthophosphoric acid and silicic acid in substantially the stoichiometric proportions of three mols of NazO per mol of P20: and one mol of NazO per two mols of 810:, the composition including starch and a wetting agent.

4. A composition for-cleaning such metals as aluminum or magnesium, which composition comprises an aqueous solution containing sodium salts of orthophosphoric acid and silicic acid in substantially the stoichiometrlc proportions of three mols of NazO per mol of PzOs and one mol of NasO per two mols of 8102, the composition includin a solvent for gums, starch, and a wetting agent.

5. A composition for cleaning aluminum and magnesium, which comprises an aqueous solution including a sodium salt of orthophosphoric acid and silicic acid in substantially the stoichiometric proportions of four mols of N820 and two mols of $10: with each moi of PzOs.

6. A composition for cleaning aluminum and magnesium, which comprises an aqueous solution including a s0d1lim salt of orthophosphoric acid and silicic acid in substantially the stoichiometric proportions of four mols of NazO and two mols of 810: with each moi of PzOs, the composition i'urther including a wetting agent.

7. A composition for cleaning aluminum and magnesium, which comprises an aqueous solution including a sodium salt of orthophosphoric acid and silicic acid in substantially the stoichiometric roportions of four mols of Nero and two mols of SiO; with each moi of PsOs, the composition ineluding starch and a wetting agent.

JOSEPH F. HART. 

